1. Field of the Invention
The present invention relates generally to the containment of wastes from industrial processes and to the stabilization and containment of drilling wastes and coal combustion residues specifically.
2. Description of the Background
The extraction of fossil fuels (e.g., coal, oil, and natural gas) from subterranean geologic formations is performed extensively around the world and provides the vast majority of the world's energy resources.
In the case of natural gas or oil, a small borehole is drilled from the surface to access the natural gas-containing formation and allow production of natural gas from the formation. Many geologic formations that contain natural gas also contain significant amounts of water that must be removed from the formation before the natural gas is able to escape to the borehole. To improve the productivity of such wells, fluids may be pumped into the formation at high pressure to create cracks or fractures in the formation, a process commonly referred to as hydraulic fracturing or simply “fracking” The natural gas escapes along these fractures thus increasing the productivity of the well.
At the present time, the state of Pennsylvania is in the early stages of what many believe to be a boom in the production of natural gas from various deep shale formations, such as the Marcellus Shale formations. Marcellus Shale is located at a depth of approximately 5,000 feet.
Drilling processes for accessing subterranean formations, including the Marcellus Shale formations, produce two primary and potentially hazardous waste streams—drill cuttings and drilling wastewater. These waste streams resulting from the drilling process used to access the formation are presenting novel and significant challenges to the state's waste disposal systems.
Drill cuttings are a mixture of soil, rock, and other subterranean matter brought to the surface during drilling of the well borehole, such as those drilled to access the Marcellus Shale. Drill cuttings are generally considered to be earthen material, however, they can become polluted when they come in contact with contamination sources common to the drilling process, such as drilling fluids or drilling mud. Drilling muds are routinely used to lubricate the drill and help remove cuttings from the wellbore. A mixture of chemicals and other constituents may be present in the drilling muds. Once drill cuttings come into contact with synthetic drilling muds or other sources of contaminants (e.g., oils and chemical additives), then the cuttings are considered to be a contaminated soil. In some instances, drill cuttings are disposed of onsite in pits or utilized in land applications. More commonly, drill cuttings are sent to landfills. Both of these disposal processes present environmental challenges and concerns.
The fluids that come back out of a well after it has been hydraulically fractured are called drilling wastewater. Wastewater is made of fluids from two distinct sources: the water that was pumped into the ground to be used to hydraulically fracture the well, and the water already present in the pores and cracks in the rock of the target formation (e.g., Marcellus Shale). There are two primary types of wastewater brine solutions generated in the shale formation gas production industry: 1) frac-flowback water, and 2) formation or produced water. Frac-flowback water is water that is returned to the surface from the well drilling and fracturing process. The flowback fluid is similar in composition to, though not exactly the same as, the fluid pumped down a well to fracture it and may contain substances such as flowback fracturing sand and other fracturing additives and chemicals. Formation water, or produced water, is the water from joints and pores in the Marcellus Shale formation itself. It was present before drilling and is removed from the geologic formation to allow efficient natural gas production from the well. Produced water is generated on an ongoing basis over the productive life of the well and contains a variety of naturally-occurring contaminants, including heavy metals, naturally occurring radioactive material, volatile organic compounds, and high levels of total dissolved solids. Because of the high salt content of the Marcellus Shale formation in particular, both frac-flowback and formation/produced water are highly contaminated saltwater that requires some form of treatment before being discharged or disposed of into the local environment.
Commonly, a chemical pre-treatment process is utilized to remove a limited number and amount of the pollutants typically present in the wastewater, resulting in a cleaner saltwater stream and a heavy metal sludge product, which is discussed further below. This process is currently being utilized to treat water for two primary purposes. The first is dilution and release of the brine water into waterways such as rivers, however, the practice of discharging treated water into waterways is currently being phased out by the Pennsylvania Department of Environmental Protection (PADEP) because of environmental concerns. The second use for chemically pre-treating the brine solution is for reuse in the fracturing process. In practice, the drilling industry finds that the chemically pre-treated water can only be reused a limited number of times in the fracturing process before it becomes necessary to dispose of the water.
Currently, the dominant technology for the treatment and ultimate disposal of water generated by the drilling process is evaporation. Evaporation is currently the only known technology used to meet many state-based dissolved solids limits for surface water discharge. Furthermore, the evaporation process generates not only clean water (which may itself be reused-/recycled for utilization in cooling towers or in the fracturing processes), but a necessary by-product is the creation of a concentrated brine solution that presents additional and unique disposal challenges. The concentrated brine solution is currently and primarily being: 1) disposed of in injection wells, 2) temporarily stored on-site in large storage tanks and lined ponds, or 3) crystallized with the intent of being used for beneficial projects such as road salt. As previously noted, the discharge of drilling fluids to surface bodies of water is not listed because it is currently being phased-out by local environmental protection departments. Additionally, the first approach (i.e., to dispose of brine solution by injection into deep well sites) has a questionable future in many areas because of the limited number of injection wells currently available due to geology-related concerns as well as recent links to earthquakes generating near injection well sites. The second approach, storing the brine in on-site tanks or ponds, offers only a temporary solution to the water issue. The third approach of a membrane- or evaporation-based treatment of the brine water followed by a crystallization process to produce solidified or highly concentrated salt products for commercial use may be utilized to treat the brine. Unfortunately, the market for beneficial salt is currently limited and insufficient to justify the significant energy requirements and capital investment required for a widespread crystallization infrastructure. Thus, these methods do not offer a long-term solution to the problem of treating large volumes of such fluids.
Concentrated brine solutions cannot be disposed of in existing solid waste landfill systems due to its high salt concentration. Any leakage or discharge of this highly concentrated brine would adversely affect the characteristics of generated landfill leachate by increasing its salinity. Standard municipal landfill facility water or treatment systems are not currently designed to accept or to effectively treat brine-based water.
As noted above, the chemical pre-treatment of brine water at centralized facilities or on-site at the well pad area produces water with minimal total suspended solids for reuse in the fracturing process. The waste streams from this process include not only the concentrated brine solution, discussed above, but also sludge, which typically contains heavy metal contaminants and radioactive particles. This heavy metal sludge, also sometimes referred to as pre-treatment sludge, is currently being sent to standard municipal landfills. However, such landfills are ill-equipped to handle this sludge due to heightened environmental risks resulting from the contaminants. In Pennsylvania, the current municipal landfills are projected to become overwhelmed in the near future as the production of gas from shale formations, and thus the waste streams associated with that production, dramatically increases.
In addition to natural gas, a second major fossil fuel used to satisfy energy needs is coal. Among many other uses, coal is typically burned at power plants to generate electricity and results in multiple ash-based waste streams. Fly ash is comprised of the fine particles that rise with the flue gas and are subsequently removed from the flue gas through various separation processes. Depending on the source and makeup of the coal being burned, the components and nature of the fly ash that is generated can vary. All fly ash, however, includes substantial quantities of toxic substances.
In addition to the fly ash removed from the flue gas, bottom ash falls directly from the combustion process to the bottom of the burner. Presently, both of these coal combustion residues (CCR) are being disposed of primarily in unlined landfills or impoundments. Even though fly ash has not previously been regulated by the U.S. Environmental Protection agency (EPA) as a hazardous waste, community and environmental organizations have documented numerous environmental contamination and damage concerns arising from CCR. For example, CCR that have not been encapsulated and are currently stored in unlined landfills have been found to leach arsenic, mercury, lead, and other toxic heavy metals into groundwater. Further, improperly constructed slurry impoundments, such as the one that failed in December 2008 in Kingston, Tenn., can spill onto and contaminate hundreds of acres of land and miles of waterways. It is anticipated that, based upon recent EPA publications, the manner in which CCR are regulated may change in the near future. The predominant thinking at this time is that fly ash and other CCR will soon be classified as a type of hazardous waste which will require that it ultimately be disposed of in lined landfill systems or that some other environmentally acceptable disposal method be utilized.
Unfortunately, as described above, there are no viable long-term solutions currently being utilized in the drilling and mining industries that provide for the environmentally acceptable and cost-effective disposal of these major waste streams produced by two major fossil fuel industries. The environmental impact of these waste streams on states such as Pennsylvania, where the related industries are active, is reaching crisis levels.